The pathogenesis of viral gastrointestinal and respiratory tract infection in man, with particular emphasis on cell-mediated immunity (CMI) is being examined. Experimentally induced influenza A infection results in blastogenic responses directed at type specific antigens such as A/matrix protein, as well as against subtype specific (hemagglutinin and neuraminidase) antigens. Lymphocytotoxic responses are even more broadly directed against target cells infected with unrelated ortho- and paramyxoviruses. The kinetics of CMI responses suggest that they may be related to early events after influenza infection and vaccination. Administration of inactivated influenza vaccines to normal adults resulted in low reactogenicity and high rate of serum hemagglutination-inhibition antibody production. The presence of pre-existing antibody protected against systemic reactions to vaccines. Split product and whole virus vaccines appeared to be of comparable immunogenicity in adults over the age of 24. Individuals between 17 and 24 years of age required a booster immunization to achieve high rates of sero-conversion. BIBLIOGRAPHIC REFERENCES: Dolin, R., Richman, D. D., Murphy, B. R., and Fauci, A. S.,: Cell-mediated immune response in influenza. J. Infect. Dis. 135: 714-719, 1977. Thornhill, T. S., Wyatt, R. G., Kalica, A. R., Dolin, R., Chanock, R. M., and Kapikian, A. Z.: Detection by immune electron microscopy of 26-27 nm virus-like particles associated with two family outbreaks of gastroenteritis. J. Infect. Dis. 135: 20-27, 1977.